1. Field of the Invention
The present invention relates to a method and a device for analyzing mutual interference due to electromagnetic induction between wirings formed in a circuit board by a computer and investigating an influence thereof. The present invention also relates to a program making a computer execute such an analysis procedure and a recording medium with the program recorded thereon.
2. Related Background Art
Conventionally, as methods and devices for analyzing mutual interference due to electromagnetic induction between wirings formed in a circuit board and investigating an influence thereof, a noise checking method and such a device described in JP2000-035984A, for example, are available.
FIG. 9 is a flowchart showing the outline procedure of conventional digital circuit design.
According to this design process, firstly, basic specifications are designed (S911). The design of the basic specifications does not involve the specific configurations of the circuit and elements and the layout of the elements. Rather, specifications required for the circuit to be designed and basic requirements for implementing the required specifications are selected and determined.
After the design of the basic specifications has been finished, based on these basic specifications, component values are set and the specific circuit configuration is designed for implementing the basic specifications (S912).
At this stage, designing resources and know-how of the past stored in the design and development department are exploited (S921).
These designing resources and know-how are stored normally in such a manner that the accumulation of past experiences and knowledge of a group and individuals is described as a document form, or such experiences and knowledge may be accumulated as tacit understanding that is not in document form.
After the setting of the specific component values and the design of the specific circuit configuration have been finished based on the basic specifications, then the layout of components and the wirings between the components are designed (S913).
At this time, in many cases, the group and persons who are in charge of the above setting of the specific component values and the design of the specific circuit configuration (S912) are different from the group and persons who are in charge of the design of the specific component layout and the wirings between the components (S913). Therefore, in order to allow such different groups and persons to share the knowledge so as to ensure the suitability and the accuracy of the design, a design instruction form (S922) is used often for the specific layout of the components and the design of the wirings between the components, where matters to be noted and to be followed are described in the design instruction form. The main contents of this design instruction form are information based on the past designing resources and know-how and information depending on specific design targets.
After the layout of the components and the design of the wirings between components have been finished, then the verification thereof is performed (S914).
A large amount of know-how (S923) is exploited also for this verification. Similarly to the above-stated past designing resources and know-how (S921), this know-how (S923) also is stored in such a manner that the accumulation of past experiences and knowledge of a group and individuals is described as a document form or such experiences and knowledge may be accumulated as tacit understanding that is not in document form.
If nonconforming parts are found by this verification (S914) (in the case of NG in S914), a modification instruction form is created (S931) and the setting of component values and the circuit design (S912) or the layout of components and the design of the wirings between components (S913) are performed again.
The modification instruction form (S931) is a document containing: information on the parts decided as nonconforming by the verification (S914); the data indicating the reason for the decision; matters to be noted for the modification; and other various information. That is to say, the modification instruction form (S931) is rich in information useful for performing again the setting of component values and the circuit design (S912) and the layout of components and the design of the wirings between components (S913) more appropriately and accurately. Such a modification instruction form (S931) also is created, in many cases, based on the past designing resources and know-how as stated above.
Based on this modification instruction form (S931) and depending on the types of the nonconformance found by the verification (S914), a determination is made as to whether the design procedure should return to the step of the setting of component values and the circuit design (S912) or the step of the layout of components and the design of the wirings between components (S913).
If nonconforming parts are not found by the verification (S914) (in the case of OK in S914), then a prototype is manufactured and is evaluated (S915).
While the verification (S914) is performed mainly by simulation using a computer, the verification at this step of manufacturing a prototype and its evaluation (S915) or later is performed using an actually manufactured circuit.
Also for this prototyping and its evaluation, many designing resources and know-how are exploited in some cases.
After the prototyping and its rough theoretical evaluation (S915) have been finished, then the prototype is activated actually so as to carry out the verification (S916).
Also for this verification, a large amount of know-how (S924) is exploited. Similarly to the above know-how (S923), this know-how (S924) also is stored in such a manner that the accumulation of past experiences and knowledge of a group and individuals is described as a document form or such experiences and knowledge may be accumulated as tacit understanding that is not in document form.
If nonconforming parts are found by this verification (S916) (in the case of NG in S916), a modification instruction form is created (S932) and the setting of component values and the circuit design (S912) or the layout of components and the design of the wirings between components (S913) are performed again.
Similarly to the modification instruction form (S931) created when the nonconformance is decided by the verification (S914), the modification instruction form (S932) is a document containing: information concerning the parts decided as nonconforming by the verification (S916); the data indicating the reason for the decision; matters to be noted for the modification; and other various information. The modification instruction form (S932) is rich in information useful for performing again the setting of component values and the circuit design (S912) and the layout of components and the design of the wirings between components (S913) more appropriately and accurately. Such a modification instruction form (S932) also is created, in many cases, based on the past designing resources and know-how as stated above.
Based on this modification instruction form (S932), and depending on the types of the nonconformance found by the verification (S916), a determination is made as to whether the design procedure should return to the step of the setting of component values and the circuit design (S912) or the step of the layout of components and the design of the wirings between components (S913). This is the same as the decision by the verification (S914) as nonconforming.
If nonconforming parts are not found by the verification (S916) (in the case of OK in S916), then the procedure goes to a mass production stage (S917) so as to complete the design procedure for the digital circuit.
When designing a high-frequency circuit with the procedure shown in FIG. 9, a serious problem occurs, called interferences due to electromagnetic induction between wirings.
When a high-frequency current flows through one wiring, a magnetic field is generated around the wiring. Along with the variation of the current at high frequencies, the magnetic field also is varied, whereby an electromotive force occurs in adjacent wirings. In other words, a signal passing through one wiring affects signals passing through adjacent wirings as noise. This is a problem of the interference between wirings.
This influence of the interference increases with increasing frequency of the current flowing through the wiring and with increasing proximity between two wirings.
Meanwhile, there are demands for electronic circuits realizing a speedy operation and miniaturization. Therefore, the electronic circuits in recent years operate at significantly high oscillation frequencies for realizing the speedy operation and are densely packaged for realizing the miniaturization. In such an electronic circuit with a high frequency current flowing through the wirings thereon and with a short distance between the wirings, the influence of the interference between wirings is considerable, thus posing a serious challenge.
FIG. 10 schematically shows an example of a portion of a high frequency electronic circuit, in which the interference may occur.
The high frequency electronic circuit shown in FIG. 10 is, for example, a part of a mobile phone, where an LSI component 955, an LSI component 956, a camera module 959 and a high frequency circuit module 954 are mounted on a board 950.
The high frequency circuit module 954 includes, as an example, an element 951 and an element 952.
The LSI component 955 and the LSI component 956 are connected via a wiring 958. An antenna 953 is connected with the high frequency circuit module 954 via a wiring 957.
The wiring 957 and the wiring 958 are disposed in close proximity to each other on the board 950 (or inside the board 950).
In such a high frequency electronic circuit, interference may occur, for example, between the wiring 957 and the wiring 958, between the element 951 and the element 952 and between the camera module 959 and the high frequency circuit module 954.
Further, in addition to between the wirings of the board 950 and between the components mounted thereon, the same problem may occur, for example, between wirings in one LSI chip and between cells connected with such wirings.
Especially, since the wirings and the cells in the LSI component 955 are arranged with a much higher density than the wirings and the components mounted on the print wiring board 950, the degree of the interference may be further increased in the former.
Thus, the design procedure shown in FIG. 9 is required to analyze the influence of the interference, e.g., between wirings by a computer at a stage before the manufacturing, for example, at the stage of the verification (S914) before prototyping.
As a conventionally available method for analyzing such mutual interference, there is a method of calculating the interference by a computer using a placement and routing CAD (computer-aided design) tool and an electromagnetic field analysis tool so as to obtain interference frequency characteristics as the analysis result.
The following describes a method of determining, by electromagnetic field analysis, an interference amount between wirings using a conventional electromagnetic field analysis tool. FIG. 11A shows an exemplary wiring pattern as a target of the analysis. A wiring pattern 1000 shown in FIG. 11A is so complicated that the electromagnetic field analysis cannot be performed for such a state of the wiring pattern. Thus, the wiring pattern 1000 is divided into a plurality of cells in a mesh form (2000) as shown in FIG. 11B. Each of the divided cells can be represented with a relatively simple analysis model. The analysis model for each of the divided cells is subjected to the electromagnetic field analysis. Thereafter, the interaction among the respective cells is calculated, whereby the electromagnetic field analysis of the wiring pattern 1000 as a whole can be performed. The interference amount between the wirings can be obtained from the result of the electromagnetic field analysis for the overall pattern.
However, in the case of the wiring pattern 1000 with a complicated structure as shown in FIG. 11A, the number of the divided cells increases as shown in FIG. 11B. Thus, the calculation time is increased enormously. As a result, the failure to complete the electromagnetic field analysis within a practical operation time will occur often. That is to say, in the case of a wiring board having a complicated structure, it is extremely difficult to determine the interference amount between wirings by electromagnetic field analysis practically.
Meanwhile, a method of checking noise flowing through a wiring with a low computational complexity is proposed (See JP 2000-035984A, for example). However, it is still difficult to analyze the interference between wirings in a wiring board having a complicated structure even by the method described in JP 2000-035984A.